The present invention relates to a copper clad laminate with a copper-plated circuit layer, and a method for manufacturing a printed wiring board using the copper clad laminate with the copper-plated circuit layer.
On manufacturing a printed wiring board comprising a fine circuit, it has been desired that the aspect ratio of the formed circuit is satisfactory. That is, the shape when the circuit is observed from the cross section is generally so-called trapezoidal, and if the upper end portion is narrower than the lower end portion, the aspect ratio becomes poor. A smaller width of the upper end portion means that the part mounting area is narrow, so that the difficulty of mounting operations redoubles.
Therefore, as a means to obtain a printed wiring board comprising a fine-pitch circuit that excels in the aspect ratio, the manufacture of a printed wiring board that adopts a so-called semi-additive method has been carried out.
In the semi-additive method as referred to here, (1) the surface of an outer-layer copper foil is exposed on the surface of a copper foil positioned on the outer layer of a copper clad laminate, by separating and removing the plating resist from the portion whereon a circuit is formed through processes of exposing and developing with the use of the plating resist, leaving only the plating resist of the portion whereon no circuits are formed on the outer-layer copper foil. Then, (2) by plating copper on the surface, the plating resist is separated and removed, and a copper-plated circuit layer is formed on the exposed surface of the outer-layer copper foil, to form a circuit pattern. (3) When plating is completed, remaining plating resist is separated, and the copper foil present on the bottom portion between the formed circuits is dissolved and removed by flush etching to complete a printed wiring board. The printed wiring boards having thus formed fine-pitch circuits have been supplied to the market.
However, in the semi-additive method as described above, when the copper foil layer is removed through flush etching, the upper edge portion of the copper-plated circuit layer is simultaneously eroded, the circuit pattern of the printed wiring board, which is the end product, is deteriorated, and the poor aspect ratio of the cross-sectional shape of the circuit has been unavoidable.
Therefore, a method for manufacturing a copper clad laminate and a printed wiring board that excels the conventional ones in the aspect ratio of the circuit pattern when processed to a printed wiring board has been demanded.